A type I ovine interferon with limited similarity to IFN-alpha, IFN-omega and IFN-tau: gene structure, biological properties and unusual species specificity.

A gene encoding a 195 amino-acid (a.a.) polypeptide with a putative 23 a.a. signal sequence that had about 60% a.a. sequence identity to ovine interferon-omega (OvIFN-omega) and 55% or less identity to BoIFN-tau, OvIFN-tau and all known IFN-alpha and -beta has been identified from an ovine genomic DNA library. Surprisingly, it shared almost complete identity to genes for rabbit IFN-omega within its coding sequence and proximal promoter region, although the two were different in their 3'-ends. This IFN (tentatively termed ovine IFN-omega variant, OvIFN-omegav), purified in recombinant form from E. coli, had normal antiviral activity when tested on sheep fetal tongue and brain cells and rabbit kidney cells, but very low activity towards bovine, goat and human cells. It competed with 125I-labeled BoIFN-tau for binding to IFN receptors on ovine cells. Expression of OvIFN-omegav was not detected by reverse transcription-PCR either in ovine peripheral blood leukocytes infected with Sendai virus, or in any other tissues examined. OvIFN-omegav may represent a previously unrecognized, non-virally inducible type I subtype distinct from IFN-alpha, -beta, -omega and -tau. The presence of a conserved gene in rabbit and sheep could reflect a recent interspecies transfer.